Remove error return value from NotifyFunc() (#4459)

It's always nil and we also forgot to check it.

Signed-off-by: Julius Volz <julius.volz@gmail.com>

cmd/prometheus/main.go

@@ -682,7 +682,7 @@ func computeExternalURL(u, listenAddr string) (*url.URL, error) {
 // sendAlerts implements the rules.NotifyFunc for a Notifier.
 // It filters any non-firing alerts from the input.
 func sendAlerts(n *notifier.Manager, externalURL string) rules.NotifyFunc {
-	return func(ctx context.Context, expr string, alerts ...*rules.Alert) error {
+	return func(ctx context.Context, expr string, alerts ...*rules.Alert) {
 		var res []*notifier.Alert
 
 		for _, alert := range alerts {
@@ -705,6 +705,5 @@ func sendAlerts(n *notifier.Manager, externalURL string) rules.NotifyFunc {
 		if len(alerts) > 0 {
 			n.Send(res...)
 		}
-		return nil
 	}
 }

rules/manager.go

@@ -573,7 +573,7 @@ type Appendable interface {
 }
 
 // NotifyFunc sends notifications about a set of alerts generated by the given expression.
-type NotifyFunc func(ctx context.Context, expr string, alerts ...*Alert) error
+type NotifyFunc func(ctx context.Context, expr string, alerts ...*Alert)
 
 // ManagerOptions bundles options for the Manager.
 type ManagerOptions struct {

rules/manager_test.go

@@ -343,14 +343,12 @@ func TestForStateRestore(t *testing.T) {
 	testutil.Ok(t, err)
 
 	opts := &ManagerOptions{
-		QueryFunc:  EngineQueryFunc(suite.QueryEngine(), suite.Storage()),
-		Appendable: suite.Storage(),
-		TSDB:       suite.Storage(),
-		Context:    context.Background(),
-		Logger:     log.NewNopLogger(),
-		NotifyFunc: func(ctx context.Context, expr string, alerts ...*Alert) error {
-			return nil
-		},
+		QueryFunc:       EngineQueryFunc(suite.QueryEngine(), suite.Storage()),
+		Appendable:      suite.Storage(),
+		TSDB:            suite.Storage(),
+		Context:         context.Background(),
+		Logger:          log.NewNopLogger(),
+		NotifyFunc:      func(ctx context.Context, expr string, alerts ...*Alert) {},
 		OutageTolerance: 30 * time.Minute,
 		ForGracePeriod:  10 * time.Minute,
 	}